Micelle and microemulsion properties of cesium di-dodecyl-dimethylsulfosuccinate, Cs-AOT

Cesium di-2-ethylsulfosuccinate (Cs-AOT) micelles in aqueous solutions and Cs-AOT/water/n-decane microemulsions were investigated, at 22 +/- 0.1 degre es C, by small angle neutron scattering (SANS). The critical micelle concen tration of Cs-AOT is similar to 2 mM, comparable to that of Na-AOT. However , their solution properties and micellar structures were found to be very d ifferent. The solubility of Na-AOT in water is approximately 1 wt %, and th e micelles grow from spherical (at a concentration of about 0.1 wt %) to ob late objects with eccentricity equal to about 0.8 (at a concentration of 1 wt %), whereas Cs-AOT is largely soluble in water, over 30 wt %, and its mi celles are disklike at 1 wt %. As the surfactant concentration increases, m icelles may go through an L-3 region, and enter the lamellar phase. Cs-AOT/ water/n-decane microemulsions, with a [water]/[Cs-AOT] = 29.1, form isotrop ic L-2 phases only at very low Cs-AOT + water volume fractions (below 0.016 5), whereas Na-AOT has a large L-2 region. These differences are probably d ue to the degree of charge condensation near the AOT polar headgroups. A th eoretical description is needed to better understand this behavior.